German Offenlegungsschrift 38 26 069 discloses already a stereoscopic microscope for the same purpose. An inversion system of a number of stereoscopically connected prisms, which system can be selectively moved into the microscope between the lens and the eyepiece arrangement in the stereoscopic beam path, ensures that a laterally inverted image standing on its head and made available by the microscope is inverted such that an upright, stereoscopically correct image reaches the eyes of the observer.
Such a prism arrangement does guarantee a compact structural length of the entire microscope; however, it is disadvantageous that the inversion system is arranged inside of the microscope; this requires significant structure and creates also technical manufacturing problems, because it must be assured that the inversion system is arranged in the beam path and is precisely oriented with respect to this beam path.
In contrast, German Patent No. 36 08 515 describes a surgical microscope, in which an attachment can be connected without any problem with the help of a quick-change mechanism, for example a bayonet lock. Such an attachment permits contact-free observation of a freely movable eye of a patient. It is designed at least in two parts of coaxial or rotationally symmetrical housing parts, which are axially movable relative to one another, and has on its side facing the eye of the patient a field-magnifying lens, which is for example moved sufficiently along the optical axis until the eye background is reflected in the eyes of the observer. If such an attachment is used in connection with the above-described inversion system, then the operation microscope offers the operator a relatively little enlarged but large-surface outer field in a stereoscopically correct view.
Of course, it can happen with this device that the field-magnifying lens hits by mistake the eye of the patient during sharp focussing; the mounting of the field-magnifying lens is for this reason, in the known design, movable with very little force. Even though with this no damage to the patient need to be feared any longer, a considerable amount of work is required in order to thereby achieve sufficient safety.
Therefore, a purpose of the invention is to avoid the disadvantages of the known microscopes and to provide instead a device of the type identified above in detail, which is suited both for the purely examining observation and also for the vision control during surgical procedures, and which device is simple in design and comfortable to handle.